Magnetic tachometer.



F. MEYER.

MAGNETIC TAOHOMETER. A1PLIOATION FILED NOV. 9, 1911.

1,058,885. Patented Apr. 15, 1913.

F ig.1

may"

UNITED STATES PATENT OFFICE.

FRIEDRICH MEYER, E soHoNEBERG, NEAR BERLIN, GERMANY, ASSIGNOR T0 .AKT.,

qEs. M x & cENEsr LIN,- GERMANY.

TELEPHON & TELEGRAPI-IENWERKE, OF SCHfiNEIBERG, BER

MAGNETIC TAGHOMETER.

Patented A rJ15, 1913.

Application filed l t'ovember 9,1911. Serial No. 659,406.

subject of the German Emperor, and residing at Schtineberg, near Berlin, Germany,

have invented certain new and useful Improvements in Magnetic Tacl1ometers,"of

which the following is" a. specification, reference being had -to the drawing forming a part thereof.

My invention relates to that class of speed- "measuring devices in which a system of permanent magnets is driven and, in consequence of eddy currents, exercises on an .in-.

dicating disk a torque which ,opposes the 'a'ct'ioi'i of a spring and is used fol indicatlng the speed of the rotating system of magnets. In m'y'magnetic tachometer I employ horse's shoe magnets mounted axially in a plate I0- tated'by the driving shaft. The north and south; poles of these hdrseshoe magnets are arranged alternately andproject a short distance beyond the. face of the plate. I obtain. the closed pathfor thelines of force.

requisitefor a powerful field by means of a second plate which is mounted on the former one; this second or upper plate is adjustable relativelyto-the other in order n that the field-can be varied for-the purpose of calibra ting the tachometer. The "indicatingdisk is mounted between the upper and lower plates. By means of this. arrangement I obtain the advantage that the entire systeitiisyery compact and,

' further," no disturbances are caused owing to the act-ionof magn'etsfof unequal strength.

One ill'ustrative embodiment of my invention is represented by way of example in the accompanying drawing, wherein F gure 1 1s-an elevation, the caslng being shown in section. For the sake of clearness both the driving 'device, audits connection with tile" shaft whose speed is to be-measure'd I are not represented. Fig. 2 is a detail top plan View showing the horseshoe magnets in their supporting plate.

Referring to 'the drawing, the plate 2 composed of non-magnetizable material is fast on the shaft 1 driven by the device whose velocity is to be measured. This plate 2 carries the horseshoe magnets 9 assembled to form a rotating system of magnets, the poles of the individual magnets 9 being placed through holes in the plate 2- and se cured in any suitablemannen- The plate 2 also carries four distance studs or posts 3' having the same e for carrying the member 4 for closing the path of the lines of force. This member may be a plate or, preferably, a ring as the latter is lighter. It will of 'cou'r e be made of lI'OIl. The studs 3 are screw-t readed so that they can be screwed into and-outof the plate 2. In this manner the distance between the poles of the magnets and the upperp ate can be adjusted as desire-d.

The indicating disk-5 which acts as an in duction disk is journaled bet-ween the magnet poles and the member 4 and is biased toward initial position by a spiralspring. 7.

Then-the disk 4 ;is rotated a,'pointer 8 is driven over a scale 10 ingll.

The advantages of .my magnetic tachometer are partly due to the form of the ro-. tating system of magnets. magnets 9., of which any desired number are,

provided on the casemployed according to the torque required to be produced, are arranged in a circle with their poles in the sat-lie sense, as will be un-- derstood from Fig. 2, so that-the adjacent, .poles of any two magnets are unlike, It is preferable so to arrange-the individual magnets that all the poles are a-t-equal distances one from another, because then the eddy currents induced in the disk 5 run' in a very short path,

Another importantfeature of my mag netic tachometer is the member 4' which closes the path of the lines of force and participates in the rotation of the system. As movements between'the iron on steel parts do not take place, neither hysteresislosses nor undesirable eddy currents in the "iron" can occur; In consequence of its being possible to vary the distance between the plate 4' and the magnets 9 the strength of field can be varied within wide limits. It is therefore possible to adjust the apparatus in an exceedingly simple manner to a predetermined torque and to equalizeinequalities produced during its manufacture.

In the example according to Fig. 1' ad justable studs are employed for mounting and adjusting the late/l. Any other means iiect may be employed for carrying this plate 4 without departing from the scope of my invention.

I claim 1. In a magnetic tachometer, the combination of a rotatable system of magnets comprising a driving shaft, a plate fast thereon The horseshoe and 'a plurality of hcrseshoe'magnets mounted parallel with the axis of and arranged wcircumterentially about the plate, an upper plate attached to the system of magnets for closing the'path of the lines of force of the same, an oscillating indicating disk between said fupper plate and the system of magnets adapted to. be rotated by eddy currents generated in the same by the system of mag 1Q nets, and means for resisting the movement.

of said disk.

'2. In' magnetic tachometer, .thecombination of a rotatable system of magnets, comprising a. driving shaft, a plate fast thereon,

and aplurality of horseshoe magnets mounted parallel with the axis of and arranged circumferentially about the plate, an upper plate adjustably attached to the system of magnets for closing the path of the lines of force of the same, an oscillating indicating disk between said upper plate and the system of magnets adapted to be rotated by .eddy currents generated in the same by the.

system of magnets, and a biasing spring resisting the movementof sa d disk. I 3. In a magnetic tachometer, the combination of a rotatable system of magnets comprising a driving shaft, a plate fast thereon, and-a plurality ofhorseshoe magnets mounted parallel with the axis of and arranged circumferentially about the plate, the poles of said magnets projecting through the plate and being directed upward, anupper plate attached tee the-systemof magnets for closing the path of the lines of force of the, same, an oscillating indicating disk between said upper plate and the system of magnets adapted to'be rotated by eddycurrents generated in the same by the system of magarranged circumfcrentially about the plate,

the poles of sad magnets projecting through the plate and eing directed upward, an up-.' per plate adju'stably attached ,to thesystem of magnets for closing the path of the lines of force of thesame, an oscillating indicating disk between said upper plate and the system of magnets adapted to be retated by eddy currents generated in the. same by the 0 system of magnets, and a biasing spring for resisting'its movement;

' In testimony whereof- I aflix mysignature in presence of two witnesses.

FRIEDRICH?MEYER: v Witnesses HEN RY HAsrER, VVOLDEMAR I'IAUP'J. 

